This invention relates to an etching method for etching a semiconductor substrate having a polysilicon layer and a silicide layer on the polysilicon layer.
In general, a semiconductor device is known which comprises a semiconductor substrate having a polysilicon layer and a silicide layer on the polysilicon layer. The silicide layer and the polysilicon layer will collectively be called a polycide layer. The polycide layer may be etched into a gate electrode by etching. It is necessary to etch the polycide layer into the gate electrode at high accuracy when the semiconductor device is an LSI.
In order to etch the polycide layer into the gate electrode at high accuracy, a conventional etching method is disclosed in Japanese Unexamined Publication Tokkai Hei 3-127826 (127826/1991) which was published on May 30, 1991. Plasma etching is used in the conventional etching method. By using a resist film as a first etching mask, the silicide layer is etched into a patterned silicide layer by an etching plasma. The etching plasma may be composed of chloride and hydrogen bromide. After removing the first etching mask, the polysilicon layer is etched into a patterned polysilicon layer by an etching gas by using an oxide film as a second etching mask. Hydrogen bromide may be used as the etching gas.
However, the first etching mask is different in material from the second etching mask in the conventional etching method. Namely, it is necessary to use at least two etching masks on etching the polycide layer in the conventional etching method. In addition, it is necessary to remove the first etching mask after etching the silicide layer into the patterned silicide layer.